Interesting little game. Why grandma only cooks using a flamethrower is beyond me, but at least this is the fastest cooking I've ever seen in a game, so that's a win for grandma. Gameplay-wise it's fun, though quite repetitive after a while. I am also surprised there is no penalty for keeping the customer waiting, which is a rare occurrence in restaurant sims like this. But overall, this is quite nice!
For criticisms, a big one is that the controls are a bit buggy, especially when you are starting to play the game quickly. I've got the game refuse to pick up the flamethrower a few times in my playthrough, and that basically means I can no longer do anything meaningful in the game. I would also say the rat is a bit too annoying, especially when it's quick to the point where you cannot NOT stop what you are doing and deal with the rat immediately. It would be nice if it's slower than you can ignore it for a while to risk it. Finally, it would also be nice if there were a timer to let the player know how long they have left in the level.
Anyway, this is quite a nice game. Good job!