Peel the avocado and place in a tall blender, immediately puree with the lemon juice (or pass through a sieve), season with garlic, salt and pepper.
Drizzle the scallops with lemon juice, season with salt and pepper. Let the lemon oil get hot in a grill pan, add the garlic clove and rosemary sprig and fry briefly. Add the scallops and fry for 2 minutes on each side.
During this time, arrange the avocado cream on the plates. Spread the fried scallops on top of the avocado cream and serve immediately.