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. Salad (without lemon zest and basil) can be made 1 day ahead. Cover and chill.