Mix garlic, oil, vinegar, oregano, and red pepper flakes in a large bowl.
Add sweet peppers, onion, artichokes, mozzarella, and salami and toss to coat; season with salt and black pepper.
Let sit, tossing occasionally, at least 15 minutes.
Zest half of lemon over salad and add basil; toss to combine.
Season with more salt and black pepper if needed.
Do Ahead: Salad (without lemon zest and basil) can be made 1 day ahead. Cover and chill.
