Why does my omelet with Velveeta froth up in the microwave?
Velveeta is a processed 'cheese' (I believe the package says something like 'processed cheese food product, which is about as far from real cheese as you can get), which means it has a much lower melting point than real cheese. In fact, I would be astonished if the melting point weren't lower than the coagulation point of eggs.

Use real cheese. And a pan. Your tastebuds will thank you for it.