Heat the olive oil in large skillet over medium heat. Cook and stir the onion and garlic in the oil until tender, about 5 minutes. Remove the onion and garlic from the pan and set aside. Crumble the pork into the skillet and cook until no longer pink. Return the onion and garlic to the skillet and stir through the pork. Season with salt and pepper. Cover the skillet and cook the mixture for 5 minutes. Stir the green bell pepper, red bell pepper, yellow bell pepper, and raisins to the mixture; cover and cook another 5 minutes. Add the spinach to the skillet and stir just before serving.