Slice the tops off of the bell peppers and remove seeds and veins.
Grate large chunks of cauliflower over a bowl, until the whole head resembles coarse rice. Squeeze out any extra moisture of the cauliflower by placing it in a paper towel or a cloth, if necessary.
Mix the veggies, flax seed, 1 1/2 cups cheese, and garlic into the cauliflower rice. In a separate bowl, mix together the ground beef and taco seasoning. Dump the ground beef mixture into the cauliflower rice mixture, and combine with your hands.
Divide mixture evening among the peppers. Pour 2 cups of water into a slow cooker, and turn it on to low. Then place the peppers into the slow cooker and cover. Cook for 4 hours.
30 minutes before you are ready to serve turn the temperature up to high. During the last few minutes of cooking, top each pepper with a remaining cheese.