Put ½ the chopped cauliflower in a food processor. Pulse until it resembles a rice consistency. Repeat with the other half of the cauliflower. You'll get about 6 cups of riced cauliflower in total.
Warm olive oil in a large skillet over medium heat. Add chopped onion. Cook on medium heat until translucent.
Add minced garlic and serrano pepper. Cook another minute longer.
Add riced cauliflower, tomato paste, salt, and pepper. Cook until tender.
Serve with chopped cilantro and limes.
Notes
This recipe will last 3-5 days in an airtight container in the fridge.