Cover the lasagna dish completely, creating as tight of a seal along the edge as possible. The greater the seal, the less chance of drying the pasta out. Place in the oven for 20 minutes. Stick a fork in the center of the lasagna, holding it there for 15 seconds. Pull the fork out and touch it. If the fork is warm, the lasagna is properly warmed. If not, put the lasagna back in the oven, checking it every 5 minutes. How to Oven Bake Lasagna.