Preheat the oven to 375 degrees.
Put the cashews in a medium saucepan and cover by 1-inch of clean water. Bring it to a boil and let it cook for 10 minutes. Drain any excess water and set aside.
Next, start cooking the quinoa in a medium saucepan. Once you have the quinoa cooking, saute the diced onions in 3-4 tbsp of vegetable broth in a separate large pan over medium heat until the onions are soft and translucent, about 8-10 minutes.
Pesto Sauce - Add the fresh basil, cashews, garlic, lemon juice, nutritional yeast, almond milk, salt, and pepper to a small blender cup and blend all the ingredients until it’s smooth and creamy. Set the sauce aside until later.
Quinoa FIlling - Once the onions are soft, add the 4 cloves of minced garlic and 2 tsp Italian seasonings to the pan, stir it around, and let it cook for a few minutes.
Add the fresh spinach, cooked quinoa, and the cashew pesto sauce to the pan with the onions and garlic. Stir to combine the filling so the pesto sauce coats the quinoa and let it cook for 2-3 minutes or until the spinach starts to wilt.
Tomatoes - 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 ½ cup of the pesto quinoa filling into each tomato and put the tops back on.
Drizzle a little bit of vegetable broth or 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. Serve and enjoy!