Nathan is SOOOOOO cute! I can understand that this is a difficult problem for you and for many mommies I know. Here are some things/ways I get my son to eat healthy items.
1. Yogurt(use Greek, full fat) parfaits. Layer the yogurt(sweetened with agave or maple syrup and vanilla) with fresh fruit and whole grains like whole wheat couscous or brown rice. I swear my son gobbles these right up! I sprinkle in flaxmeal and sunflower seeds(I don't knwo if your little guy is too little for that) to up the nutritional ante.
2. Steel Cut Oatmeal: whole grain and DELICIOUS! I have a recipe for it on my site. Sometimes, I mix in pumpkin for a veggie and sprinkle with pumpkin pie spice instead of your standard oatmeal flavors. This is great for breakfast or a snack. You can make it ahead of time and gently reheat and add milk throughout the week. Smash walnuts finely and add to it for Omega 3's and extra good fats and protein.
3. Avocado toast: spread mashed up avocado with a pinch of salt and pepper on toast. You can even finely chop or add pureed veggies to it. My son loved this even when he was going through a super picky phase.
4. Smoothies: you can add fish oil/flax to them along with yogurt(fat and protein) and a big handful of spinach for something green! If he objects to the color, add blueberries for a beautiful purple drink.
5. Does he like to dip? Try lightly steamed veggies with light ranch, guacamole, etc. My son will eat more veggies this way than anything else.
6. Roasted root vegetables. These are naturally sweet, but healthy.
7. Try steaming and pureeing veggies like sweet potato, carrots, squash, spinach, etc. It is very easy to hide them in pasta sauce, muffins, pancake mix(we love sweet potato pancakes), or even soups.
Several of these items can be found on my site for directions if you need them. Just keep trying, it can take children a really long time to develop a taste for healthy foods!