Combine all ingredients in a bowl, then taste and adjust seasoning with salt and pepper as needed.
Refrigerate for at least 10 minutes to allow the flavors to meld together.
Shrimp:
In a large skillet, heat olive oil over high heat. Sprinkle chili powder and salt on both sides of the shrimp. Arrange the shrimp in a single layer and cook for 2-3 minutes on each side, or until they turn pink and are fully cooked.
Warm the tortillas, then fill each with a portion of shrimp.
Cilantro Lime Rice:
Place the rice in a mesh strainer and rinse under cold water, until the water runs clear. Drain well and set aside.
In a medium saucepan with a lid, butter over medium heat. Once hot, add the rinsed rice and chopped onion. Stir frequently and cook until the rice turns from translucent to bright white and the onion softens.
Add the minced garlic and stir for about 30 seconds, just until fragrant but not browned.
Pour in the chicken stock. Add salt and stir, then reduce the heat to the low. Cover with a lid and let it cook for 15 minutes.
Remove the pan from heat and let it sit, still covered, for 10 minutes.
Once fully cooked, drizzle the lime juice over the rice and sprinkle with chopped cilantro. Use a fork to fluff the rice and mix in the lime juice and cilantro. Assemble bowls with shrimp, mango salsa and avocado slices.