Heat olive oil in a large skillet over medium-high heat until shimmering.
Add diced onion and cook for 2-3 minutes until softened, then add minced garlic and cook for 30 seconds until fragrant.
Add riced cauliflower, cumin, chili powder, salt, and pepper to the skillet and cook for 5-7 minutes, stirring occasionally, until cauliflower is tender and slightly golden.
Stir in diced tomatoes and cook for 1-2 minutes until heated through.
Remove from heat and stir in fresh cilantro and lime juice before serving.