Make the pickled onions: Place the onion in a bowl or jar. In a small saucepan, combine the vinegar, ½ cup water, sugar and 1 teaspoon salt. Place over medium heat and cook, stirring, until the sugar and salt dissolve. Pour over the onions. Let cool, cover and refrigerate. (You can make this up to 2 days ahead; keep covered and refrigerated.)
Make the crema: In a small bowl, whisk together the sour cream, lime zest and juice, garlic powder and honey. Season with salt and pepper. (Yield: Scant ½ cup. You can make this up to 1 day ahead; keep covered and refrigerated. Whisk before using.)
Warm the avocado oil in a large skillet over medium heat. Add the chorizo and cook, stirring and breaking it up, until cooked through and browned in spots, 7 to 10 minutes.
Divide the rice among 4 shallow bowls. Using a slotted spoon, divide the chorizo among the bowls. Divide the radishes and avocado among the bowls. Add some of the pickled onion to each bowl. Drizzle each bowl with crema and sprinkle with cilantro and pepitas. Serve.