In shallow bowl, combine buttermilk, garlic, pepper, and salt. Place potato flakes in another shallow bowl. Dip fish fillets into buttermilk mixture, shaking off any excess liquid; then dredge in potato flakes. Repeat to coat all fillets.
Melt butter in a large nonstick skillet over medium-high heat. Add fish and cook 3 to 5 minutes on each side, or until fish is golden and flakes when tested with a fork. Squeeze juice of 1 lemon wedge over each fillet.