Heat 2 teaspoons of olive oil over medium-high in a large saucepan or lidded skillet. Add the diced zucchini and cook, stirring occasionally, 5-7 minutes or until golden brown in spots and just tender. Lightly sprinkle with salt and pepper as the zucchini cooks. Remove to a plate.
Add another teaspoon or two of oil to the pan, as needed, and then reduce the heat to medium and add the onion and optional bell pepper. Sauté until softened, 2-3 minutes, and then add the beef. Brown the beef, crumbling as you go. When the beef is nearly browned, add salt and pepper to taste (I add about 1/2 teaspoon of kosher salt and several more turns of the pepper mill at this point) along with the cumin and garlic powder.
When the beef is cooked, stir in the salsa, cover the pan, and cook over medium heat for 8 to 10 minutes to allow the flavors to blend. (I stir once midway through and adjust the heat to low if the mixture seems nicely thickened.)
Add the zucchini back to the pan and cook, covered, to heat throughout, for another 2 minutes or so.
Sprinkle with cheese, if using, and serve with additional toppings as desired.