A fun idea and cute art! Reminds me of some of those feed the holes games, but kaiju style.
I think the eating can feel a bit clunky. Maybe I would do something like this:
Make it so when the player holds left click the kaiju just keeps it's mouth open and sucks things in front of him into his mouth. Instead of having to click each time to eat something. In my opinion, this would make it look and feel way more satisfying and less clunky.
Super cute idea! Fun game. I think I reached the end of the evolutions because I filled up the bar twice, but there was no animation and the bar got longer.