Heat oven to 400°F.
Toss cauliflower florets with oil and taco seasoning.
Spread out on a sheet pan.
Roast cauliflower, shaking the pan halfway through cooking, until cauliflower is tender and golden, 25 to 30 minutes.
While cauliflower cooks, make avocado crema.
Combine avocados, cilantro, sour cream, salt, water, and lime juice in a food processor.
Blend until smooth.
Add more water, if needed, until the crema is still thick but pours easily off a spoon.
Taste the crema and add some more lime juice or salt, if needed. If you’d like some spice add a pinch of cayenne pepper or some hot sauce.
When the cauliflower is done roasting, warm the tortillas.
You can do this by covering the tortillas with a slightly damp paper towel and microwave until warm, 15 to 20 seconds.
Alternatively, you can warm the tortillas over the burner of a gas stove for a few seconds on each side to lightly blacken them in spots.
Set out the cauliflower, tortillas, and toppings to assemble tacos at the table.