How Soaps Work

Soaps work because of the difference between the two ends of the same soap molecule. The long carbon chain is hydrophobic meaning it is repelled by water molecules, and the head is hydrophilic meaning it is attracted to water molecules. So, in that case of oil in water, the hydrophobic tails point towards the oil in the middle forming a circle around it, with the hydrophilic heads pointing out towards the water. 

These circles are called micelles, and it is because of these micelles that oils (which normally repel water) can be dissolved and washed away by soapy water.

Oven cleaners take advantage of this, plus the process of saponification, whereby fats and oils are turned into soap by a strong base.

You may recall that fats, or triglycerides, are three fatty acid carbon chains connected by a glycerol.

Glycerol, a fatty acid's carbon chain, and a triglyceride.

When a strong base is added to a triglyceride it breaks into glycerol and three fatty acid salts (i.e. soap molecules). Because each of these salts has a hydrophilic side, they can form micelles and be easily washed away with water.

So, while oven cleaners are not themselves soaps, they are strong bases, which when added to a greasy oven creates soaps that are then easily wiped away with a wet cloth.