How to Make It
Preheat oven to 400°F.
Place walnuts in a large ziplock plastic freezer bag. Seal bag, and crush gently with a mallet or heavy pot until nuts break into small pieces. (Do not overcrush nuts.) Combine nuts and thyme in a shallow dish. Place flour in a separate shallow dish. Combine Dijon and egg white in a third shallow dish.
Press tops of fillets in flour; shake off excess. Dip floured side of fillets in egg mixture; shake off excess. Sprinkle fillets with salt and pepper. Dip egg side of fillets in walnut mixture, pressing to adhere.
Heat oil in a large ovenproof nonstick skillet over medium. Place fillets, walnut side down, in skillet. Cook until walnuts are golden and toasted, 3 to 4 minutes. Turn fish. Bake at 400°F until fish flakes easily with a fork, 4 to 5 minutes. Serve with lemon wedges.