Preheat the grill for high heat. 

Chop the white onion, jalapeno and bell pepper.  Season with salt, pepper and garlic powder. Add the olive oil to a cast-iron skillet and place on the grill. Grill for 10 minutes. 

Brush the corn with the vegetable oil. Grill the corn completely, making sure it is lightly charred on all sides. Cool and cut the corn off the cob. 

In a bowl, combine the corn kernals, white onion, jalapeno, bell pepper, mayo, sour cream, lime juice, chili powder, cayenne pepper, garlic salt, and hot sauce. Mix until well combined. 

Pour into serving bowl and garnish with queso fresco, fresh cilantro and avocado slices. Serve warm or at room temperature.