Heat butter in a large skillet over medium-high heat.
Dredge tilapia fillets through flour and sprinkle each with lemon pepper seasoning, then add them to the melted butter in the skillet. Cook for 3-4 minutes on each side until the tilapia is cooked through and flakes easily. Remove from heat and set aside. In the heated butter, add in sliced lemons and cook for 2 minutes on each side, until they start to brown.
Add the tilapia back to the skillet and drizzle with lemon juice, cooking for 1-2 more minutes. Serve warm.