For the rings, peel the onions and cut them into thick slices (approx. 2 cm). Remove about 20 large rings with 2-3 onion layers each. Wrap 1 bacon slice around each onion ring. Fix with a wooden skewer.
For the dip mix mayonnaise, Sriracha and lime juice. Season to taste with salt and pepper.
Grill the onion rings on the hot grill for about 5 minutes on each side. Serve with the dip.