Mix: Stir the almond flour, Parmesan, egg, grated onion, garlic, parsley, oregano, salt, and pepper together, then gently mix in the turkey. Roll into about 20 meatballs with wet hands.
Brown: Brown the meatballs in hot olive oil in a 12-inch skillet, 5 to 6 minutes. Transfer to a plate.
Simmer: Cook the diced onion 3 to 4 minutes, add garlic and pepper flakes, then the tomatoes, basil, and salt. Return the meatballs, cover, and simmer 12 to 15 minutes, to 165°F (74°C).
Finish: Fold in the spinach until wilted, then top with Parmesan, basil, and a drizzle of olive oil.