Stuffed Bell Peppers

bell peppers, any color

olive oil, plus more for drizzling 

lean ground beef 

Kosher salt and freshly ground black pepper

onion, finely diced 

garlic, chopped

medium zucchini, finely diced 

Roma tomatoes, seeded and finely diced 

Red pepper flakes, as needed 

cooked long-grain and wild rice 

grated pepper Jack cheese