In a small pot with a lid over high heat, warm the oil. Add the salt and rice and stir to coat the rice and toast it slightly.
Add the water to the pot. As soon as the water boils, turn the heat down to a low simmer and place the lid on the pot. Cook, without lifting the lid for 15 to 18 minutes. Marinate the shrimp while the rice is cooking.
Remove the cooked rice from the heat and set it aside to rest and cool down with the lid on. When the rice is cooled, fluff with a fork and stir in the lime juice and cilantro.
Shrimp
In a large bowl, whisk together the olive oil, cumin, chili powder, oregano, garlic powder, salt, pepper, and cayenne.
Add the shrimp to the bowl and toss to coat completely. Set this aside for 15 minutes while you make the crema.
In a large skillet over medium heat, sauté the shrimp until just opaque, approximately 3 minutes per side. Add the lime juice to the cooked shrimp and remove the pan from the heat.
Crema
In the bowl of a food processor, add the avocado, lime juice, jalapeno pepper, garlic cloves, and cilantro. Process until creamy. Stir in the sour cream and season with salt and pepper to your liking.
Burritos
In a cast iron skillet over medium heat or a 250°F oven, warm the tortillas.
Place 1/4 cup of the rice in the center of each tortilla. Place 1/4 of the shrimp on top of the rice. Spoon or drizzle crema over the shrimp. Top that with shredded lettuce. Add spoonsful of pico de gallo or salsa, if using.
Fold two opposite sides of the burrito towards the filling. Roll the tortilla away from you to tightly wrap the filling.
Using a sharp serrated knife, slice the burritos in half and wrap them in foil or parchment paper for eating with your hands. Serve with your favorite hot sauce on the side.