Finely chop enough of the onion to yield 1 tablespoon. Toss with the grapes and 1 tablespoon olive oil; season with salt and pepper.
In a large skillet, heat 1 tablespoon olive oil over medium-high heat. Add the kielbasa and cook until browned, 3 to 4 minutes. Add the bell peppers and the remaining onion slices; season with salt and pepper. Cook, stirring, until golden-brown, 7 to 8 minutes. Transfer to a large plate.
In the same skillet, heat the remaining 1 tablespoon olive oil over medium heat. Add the eggs, season with salt and pepper and scramble, 2 to 3 minutes. Stir in the kielbasa mixture and 1/2 cup cheese.
Divide the egg mixture among the tortillas and roll up burrito-style. Transfer the burritos to plates and top with the remaining 1/2 cup cheese and the salsa; serve with the grape relish.