3 tablespoons extra virgin olive oil, divided
6 garlic cloves, minced
1 medium onion, finely chopped
1 teaspoon dried basil
3 5-ounce containers baby spinach
1/2 teaspoon salt, divided
1/4 teaspoon pepper, divided
1 cup fresh breadcrumbs
1 cup shredded Asiago cheese
1/4 cup grated Pecorino Romano cheese
1 pound mixed sweet mini peppers, halved lengthwise and seeded