Prep the produce: remove the green leaves and stem from the 1 large head cauliflower and cut it in half, then grate the cauliflower using a box grater or food processor; chop the 1 yellow onion; mince the 6 cloves garlic; seed and finely chop the 1 jalapeño; chop the 2 cups tightly packed kale leaves so they will easily mix in later.
Heat a large skillet over medium-high heat and add 2 Tbsp avocado oil.
Add the chopped onion and sauté, stirring occasionally, until softened and fragrant, about 5 minutes.
Add the seeded, finely chopped jalapeño and the minced garlic; sauté, stirring, until fragrant, about 2–3 minutes.
Add the grated cauliflower to the skillet and cook, stirring frequently, until it begins to brown and reduce in volume, about 5–8 minutes.
Stir in 1 14.5-oz can diced tomatoes, 1 tsp kosher salt (or to taste), and 1.5 Tbsp chili powder; cook, stirring occasionally, until much of the tomato liquid is absorbed, about 5 minutes.
Add the chopped kale leaves, stir to combine, and cook until the kale turns bright green and is wilted, about 3 minutes.
Taste and adjust salt if needed. Serve warm, optionally with cherry or grape tomatoes.