Whisk the eggs and half-and-half together in a bowl until frothy. Set aside.
Heat the olive oil in an oven-proof, 10-inch, nonstick skillet over medium heat.
Add the onion and sauté until soft and translucent, 3 to 4 minutes. Add the bell pepper and zucchini and continue cooking until the vegetables are tender, 3 to 4 minutes longer. Season to taste with salt and pepper.
Add the tomato and continue cooking until slightly softened, then taste and adjust the seasoning as needed. Distribute half the cheese over top of the vegetables, then stir in the eggs.
Using a rubber spatula, continue to stir and scrape the bottom of the pan until the eggs form large, wet curds, 2 to 3 minutes. Smooth the mixture so it's evenly distributed in the pan and stop stirring for about 30 seconds to allow the bottom to set. Sprinkle with the remaining cheese.
Bake until the cheese has melted and the frittata is slightly puffed and golden, 5 to 7 minutes. Remove from the oven and let stand for about 5 minutes. Use a spatula to loosen the frittata around the edges and gently slide it onto a serving platter.