In a skillet, preheat 3 tablespoons oil oil for a few minutes at medium heat.
Once the oil is hot, add the beef. Season to taste with salt and pepper. Stir as needed and brown for 6-8 minutes.
Add the onion, garlic, 1 minced serrano and diced bell pepper. Season lightly with salt and pepper and continue cooking for 3-4 minutes.
In the blender,. add the tomatoes, 1 reserved serrano, oregano, 2 teaspoons beef bouillon, 1/2 cup of water, 1/3 tsp pepper and salt to taste. Blend on high until smooth. Pour into skillet with beef.
Stir beef with blended tomato sauce well. In the jar of the blender, add 1 1/2 cups of water. Pour into skillet. Bring up to a simmer and taste for salt. Stir and continue cooking for 10 minutes.
After 10 minutes, add the zucchini, cilantro and 1 remaining serrano. Reduce to a simmer, cover and continue cooking for 15-20 minutes.
Ladle into shallow bowls and serve with rice, beans and warm corn tortillas on the side.