Combine thyme, rosemary, garlic and oil in a pot just wide enough to hold fish in a single layer without touching. (When fish is added, oil should cover it, so it is better to use more oil than not enough.) Peel 1 lemon, using a vegetable peeler to remove yellow part only, in strips. Add peel to oil. Season fish on both sides with salt and pepper.
Fit skillet with a deep-frying thermometer and heat oil to 180 degrees over medium-low heat. Reduce heat and monitor temperature, adjusting until temperature is a stable 180, with small bubbles occasionally rising to surface.
When temperature is stable, add fish. Oil temperature will drop, so raise heat slightly (never above medium-low) just until it reaches 180 again; then reduce.
Cook fish 13 to 15 minutes, until top is completely opaque and flakes easily with a fork. Remove to a plate lined with paper towels, let drain. Place on serving platter, sprinkle with herbs, and serve immediately with lemon wedges.