1. In a small bowl, mix together sugar and 1/4 cup coarse salt. Cut 2 lemons in half crosswise, remove any visible seeds, and transfer to a small container. Add sugar and salt mixture and one sprig of thyme. Cover and refrigerate for at least 6 hours and up to 1 week.

2. Coarsely chop remaining lemon and 6 cloves of garlic and place in a medium bowl; toss to combine. Divide lemon and garlic mixture evenly and add to the cavity of each fish, along with 1 sprig of thyme; set aside.

3. Finely chop remaining 2 cloves garlic and thyme leaves. Add to a small bowl with olive oil; whisk to combine.

4. Preheat a grill pan over high heat. Brush fish with olive oil mixture and season with salt and pepper. Place fish on grill and cook, turning once, until the thick, fleshy part is firm to the touch, about 8 minutes per side, brushing occasionally with olive oil mixture.

5. Remove lemons from sugar and salt mixture. Brush off any excess sugar and salt and place on grill, flesh side down. Cook until lemons are charred. Remove fish and lemons from grill. Serve immediately with escarole and a sprinkling of sea salt.