Preheat the oven to 375 degrees.
Put the cashews in a medium saucepan and cover by 1-inch of water. Bring it to a boil and let it cook for 10 minutes. Drain any excess water and set aside.
Cook the quinoa according to package instructions in a medium saucepan.
While the cashews and the quinoa are cooking, saute the diced onions in vegetable broth or oil in a large pan over medium heat for 10 minutes or until they are soft and translucent.
Add the fresh basil, cashews, garlic, lemon juice, nutritional yeast, almond milk, salt, and pepper to a small blender cup and blend until it’s smooth and creamy.
Once the onions are soft, add the minced garlic and Italian seasonings to the pan, stir, and let it cook for a few minutes.
Add the fresh spinach, cooked quinoa, and the pesto sauce to the pan with the onions and garlic. Stir to combine the filling so the sauce coats the quinoa and let it cook for a few minutes or until the spinach starts to wilt.
Cut the top of the tomatoes. Use a grapefruit spoon (with a serrated edge) to gently slip into the tomatoes and scoop out all the seeds and membranes. Be careful not to break through the tomato skin and make a hole.
Spoon the filling into each tomato up to the top and put the tops back on.
Add a little bit of water into the bottom of a medium casserole dish to stop the tomatoes from sticking to the bottom. Place the stuffed tomatoes in the baking dish and then bake it for 30 minutes or until the skin starts to blister.
Carefully remove the tomatoes from the oven and let it cool for a few minutes before you garnish with fresh basil.