Combine tomatoes, corn, cumin, chopped chipotles or ancho paste and the chopped cilantro in a medium sized bowl. Set aside.
Use a 2-quart microwave-safe dish with a lid and combine the potatoes, shallots, and oil and season with salt and pepper. Spread the potatoes in an even layer to promote even cooking.
Cover then microwave on high for 6 minutes.
Place the fish in a single layer around the edge of the dish atop the potatoes. Season with salt and pepper. Spoon the tomato mixture in the center. Microwave on high until the fish is cooked through and potatoes are tender -- about 9 to 10 minutes.
Remove from microwave and mix carefully to combine but don't break up the fish. Garnish with cilantro and a dollop of Mexican Crema OR Greek Yogurt.