In a food processor fitted with the s-blade, pulse the pepitas and sun-dried tomatoes until they are finely crumbled and no large pieces remain. Set aside to a small bowl.
Using the shredding blade for the food processor, shred the cauliflower, mushrooms, onion, garlic, and carrots.
Heat a large, deep skillet to high heat.
Add the shredded vegetable mixture and cook until all of the vegetables are soft and the cauliflower is no longer white and opaque, about 8-10 minutes. If any liquid remains in the pan, continue cooking until it has evaporated and the mixture seems somewhat dried out and not mushy.
Reduce the heat to low and add the pepita/sun-dried tomato mixture. Cook for 1-2 minutes, stirring to combine and warm through.
Set aside 2 cups and transfer the rest to the fridge or freezer for future meals. (see notes for options)
Add the reserved mixture back into the pan and add the taco seasoning along with a 1/2 cup of water.
Bring to a boil, then reduce to a simmer for 2-3 minutes.
Add the refried beans and stir to combine.
Warm the corn tortillas until soft and pliable. I like to wrap them in a clean kitchen towel dampened on all sides with a bit of water, then microwave for 2 minutes. The towel will be hot so use a hot pad to remove it from the microwave.
Using a small cookie scoop or spoon, measure about two tablespoons of filling onto a tortilla, then roll up tightly, pushing the filling to each edge as you go. Place seam side down on a large rimmed sheet pan. Repeat with the remaining tortillas and filling.
Bake at 425F for 20 minutes, or until slightly browned and crispy. Check at the 10- and 15-minute marks to make sure they are not browning too quickly.