Remove stem and trim leaves from cauliflower. 

To shred the cauliflower into rice using a box grater: cut cauliflower into large chunks, then grate into rice using the medium-sized holes.

To shred the cauliflower into rice using a food processor: cut cauliflower into small pieces, attach the grater attachment to food processor, and feed cauliflower into processor to shred. 

Heat olive oil in a large nonstick sauté pan over medium-high. Add onion and cook until softened and starting to turn golden brown, 3–5 minutes. 

Stir in tomato paste, garlic, oregano, cumin, cayenne, and paprika; cook 1 minute. Add drained tomatoes and cauliflower; toss to combine. Cover skillet with a tight fitting lid and let steam until tender, 5–8 minutes.

Remove from heat and stir in ¾ teaspoon salt; season with additional salt and black pepper to taste.