Oh, and how's your overall appetite?  Is needing to put on some pounds complicated by any lack of appetite?  

Okay, so, have you tried this?  It's high in protein, and may work well as a supplement to your regular diet.  

I'd second all of Zorba's suggestions, and add some ideas from when my picky-eater kids were little:

Peanut butter and butter sandwiches
Half and half or cream on cereal instead of milk.
"milkshakes" made with ice cream and cream
Avocado toast

Family favorite: steak sliced thin and piled on rolls dipped in butter. yum.

Also - found this on Sloan-Kettering's website, intended to help people undergoing cancer treatment who need to put on or maintain their weight:

Don't eat foods that are fat-free or reduced in fat. Avoid food and drink labels that say "low-fat," "non-fat," or "diet." For example, use whole milk instead of skim.

    Snack on dried fruits, nuts, or dried seeds. Add them to hot cereals, ice cream, or salads.

    Drink fruit nectars or fruit shakes.

    Add butter, margarine, or oils to potatoes, rice, and pasta. Also add them to cooked vegetables, sandwiches, toast, and hot cereals.

    Add cream cheese to toast or bagels or use it as a spread on vegetables.

    Spread cream cheese and jam or peanut butter and jelly on crackers.

    Add jelly or honey to breads and crackers.

    Mix jam with diced fruit and use it as a topping over ice cream or cake.

    Snack on tortilla chips with guacamole. Add avocado slices to your salads.

    Use high-calorie dressings on salads, baked potatoes, and on chilled cooked vegetables, such as green beans or asparagus.

    Add sour cream, half and half, or heavy cream to mashed potatoes and cake and cookie recipes. You can also add it to pancake batter, sauces, gravies, soups, and casseroles.

    Top cakes, waffles, French toast, fruits, puddings, and hot chocolate with whipped cream.
    Make vegetables or pasta with cream sauces.

    Use mayonnaise, creamy salad dressing, or aioli sauce in salads, sandwiches, and vegetable dips.

    Mix granola with yogurt or put it on top of ice cream or fruits.

    Top your ice cream or unfrosted cakes with sweetened condensed milk. Combine the condensed milk with peanut butter to add more calories and flavor.

    Add croutons to your salads or omelets.

    Include bread stuffing as a side dish with your meals.

    Drink homemade shakes. Try the shake recipes in the "Recipes" section. You can also drink high-calorie, high-protein drinks, such as Carnation® Breakfast Essentials or Ensure. See the next section for a list of nutritional supplements you can buy.

There are a bunch of recipes further down that page that may give you some ideas, too.

http://tinyurl.com/y79ksu4d

Many of the foods like Quinoa, high calorie fruit, avocados and nuts can be added to other foods like oatmeal, salads etc. to increase calorie count.

Here is a link to article on uses of Quinoa which can be fixed in larger amounts and stored to use as desired as an additive:

http://tinyurl.com/yd5el7g3