Place a sauce pan on medium heat. Add blueberries, smashing them with a wooden spoon. After blueberries are smashed, add garlic. Once mixture starts to simmer, add balsamic vinegar and mint. Let simmer for about 10 more minutes.
Preheat oven to 400 degrees.
Place cauliflower steaks in a glass pan coated with cooking spray.
Pour blueberry sauce on top of steaks, and use a brush to coat each side with it.
Bake for 25 minutes, then take out of oven and flip. Bake for another 10 minutes.