Use an oil mister filled with a high smoke point cooking oil (like grapeseed or olive oil—light, not extra-virgin) to coat a large baking sheet. Place the polenta slices on the sheet and spray the tops with additional oil. Bake for about 30 minutes, flipping halfway through cooking time, until the polenta is crispy and golden brown on the edges.
While the polenta is baking, start the sautéed veggies. Heat the oil in a large skillet over medium-high heat. Add the onion and cook until softened and starting to brown, about 5 minutes. Stir in the garlic, cumin, chili powder, oregano, and cayenne; cook for about 30 seconds, until fragrant. Add the zucchini and red pepper to the skillet and cook, stirring often, about 3 minutes more, until slightly softened. Remove from heat and season with salt and pepper.
Combine the beans and salsa in a small saucepan over medium heat and cook until warmed through, about 5 minutes.
Divide the polenta slices onto 4 plates, then top each with salsa beans, veggies, and queso fresco. Serve with chopped cilantro, lime wedges, and additional salsa.
If you don't have an oil mister, you can brush the baking sheet and polenta with oil or use cooking spray. Shredded jack cheese can be substituted for the queso fresco if you have it on hand.