Heat oven to 400. Line a rimmed baking sheet with parchment paper.
Peel and thinly slice onions. Toss the onions with whole garlic cloves, olive oil, salt and 2 tablespoons of water on a baking sheet. Don’t spread out the onions too much to prevent browning.
Bake, stirring every 10 minutes, until softened, about 45 minutes total.
Transfer garlic cloves to a cutting board and smash with the flat side of your knife, forming a paste. Roughly chop up the carmelized onions and transfer to a serving bowl with the garlic.
Mix in yogurt, lemon juice, cayenne, salt and pepper. Add some everything bagel seasoning if you’re feeling it! Refrigerate for at least 2 hours for maximum flavor. But if you serve right away, no one will fault you.