Heat 2 tablespoons oil in a large nonstick skillet over medium-high. Add potato cubes in a single layer; cook, without stirring, 5 minutes. Stir in onion, paprika, cayenne pepper, and 1/2 teaspoon salt. Cook, stirring occasionally, until potatoes are crisp on the outside and tender inside, about 5 minutes. Remove from skillet (Do not wipe skillet clean.) Add remaining 1 tablespoon oil to skillet; swirl to coat. Add mushrooms; cook, stirring occasionally, until lightly browned, about 5 minutes. Add kale and 1/8 teaspoon salt; cook, stirring occasionally, 5 minutes. Return potato mixture to skillet; stir to combine. Keep warm. Stir together scallions, lime juice, jalapeño, and remaining 1/8 teaspoon salt in a small bowl. Heat tortillas according to package directions. Spoon a scant 1/3 cup potato mixture onto each tortilla; top each with 1 tablespoon cheese. Divide avocado slices evenly among tortillas, and serve with scallion relish.