This appetizer is so fast and easy, you can have it on the table within 10 minutes of walking in the door. Save any leftover oil, which has been flavored with the red pepper flakes and garlic, for another use like salad dressing.
Preheat oven to 400°. Drain 4 oz. olives and place on a cutting board. Lightly smash with the heel of your hand just to break apart skin and flatten slightly.
Smash 3 garlic cloves and peel.
Using a vegetable peeler, remove peel from 1 lemon in long wide strips.
Cook lemon peel, olives, garlic, ½ cup oil, and ½ tsp. red pepper in a small saucepan over medium-low heat, swirling occasionally, until garlic is sizzling and golden around the edges, 5–7 minutes.
Meanwhile, crumble 3 oz. feta into a shallow serving bowl.
Pour oil mixture over feta. Let sit at least 10 minutes and up to 1 hour.
Meanwhile, tear bread into large pieces and place in oven directly on rack. Bake until craggy edges are golden, 5–8 minutes. Serve with marinated feta and olives for dipping.