Heat olive oil in a large skillet over medium high heat. Add mushrooms and onions, stirring occasionally, until mushrooms have softened, about 8 to 10 minutes. Stir in garlic, Italian seasoning and chili flakes. Cook until fragrant. Remove from heat. Cool mixture.
Pulse pepitas in food processor until finely ground. Add mushroom mixture and half of cooked lentils. Pulse 5 to 8 times or until finely chopped. Transfer to mixing bowl.
Add remaining cooked lentils, cooked quinoa, flour, cheese and parsley. Mix to combine. Season to taste with salt and pepper.
Shape into 16 balls.
Spray skillet with olive oil cooking spray.
Cook half of meatballs, using a spatula to gently release meatballs from pan. Turn meatballs occasionally, until golden brown, about 8 to 10 minutes. Repeat with remaining meatballs.
Cook pasta in large pot of boiling water salted water, just until al dente. About 8 to 10 minutes. Drain. Heat pasta sauce in medium saucepan, over medium heat, until warm. Add in the baby spinach and heat until the spinach is cooked through - 3.5 min.
Place serving of pasta on dinner plate. Top with several meatballs, marinara, basil and 1 tbsp shredded parmesan cheese per serving