Combine the cornstarch and lemon juice until it is heated through and thickened to form a paste.
Allow the mixture to cool to room temperature.
Add in the liquid dish soap, and stir to combine thoroughly.
Slather the mixture into the oven so it covers the surface being cleaned.
Allow the DIY natural oven cleaner solution to settle for 15 to 30 minutes.
Wipe clean with a damp cloth.
Finish with a distilled white vinegar spray rinse (optional).