In a large skillet, heat the olive oil over medium heat. Add the diced onion and minced garlic, sautéing until the onion is translucent (about 3-4 minutes).
Increase the heat to medium-high and add the ground beef. Cook until browned, breaking it up with a spatula (about 5-7 minutes). Season with salt, pepper, oregano, and paprika.
Stir in the diced zucchini and chopped bell peppers. Cook for another 5-6 minutes until the vegetables are tender.
Fold in the spinach and cook until wilted, about 2 minutes.
If desired, sprinkle the shredded cheese over the top, allowing it to melt for an extra layer of flavor.
Remove from heat and let rest for a couple of minutes before serving.