Remove zest from lemons in large strips with a vegetable peeler and cut any white pith from strips with a sharp knife. Cut enough zest into julienne strips to measure 1/4 cup. Blanch zest in boiling water 1 minute, then drain in a sieve and plunge into a bowl of cold water to stop cooking. Drain and pat dry.
Squeeze enough juice from lemons to measure 6 tablespoons. Whisk together lemon juice, honey, salt, and pepper, then add 1/2 cup oil in a slow stream, whisking until emulsified.
Prepare charcoal or gas grill for cooking.
Brush both sides of bread slices with remaining 1/4 cup oil and season with salt and pepper.
When fire is hot (you can hold your hand 5 inches above rack for 1 to 2 seconds), grill bread on lightly oiled grill rack, turning once, until golden, about 3 minutes total. Immediately rub 1 side of each slice with garlic.
Toss mesclun with tomatoes, half of zest, and enough dressing to coat, then season with salt and pepper.
Put toasts on salad plates and spoon some of remaining dressing over each. Layer cheese and salad alternately on each toast and sprinkle with remaining zest.
Cooks' note: ·Zest can be blanched (and dried) 1 day ahead and chilled, wrapped tightly in plastic wrap.