Combine mayonnaise, smokey paprika and cayenne pepper in a small bowl. Stir to combine. Add mushrooms and toss to coat.
Combine panko crumbs and garlic powder in a bowl. Add mushrooms, a few at a time and toss to coat. Remove mushrooms and set aside while you repeat this process for the remaining mushrooms.
Place oil in a deep saucepan and heat over medium to high heat without bringing to the boil. Be careful to monitor the temperature. If the oil starts to bubble or smoke, take it off the heat and allow it to cool slightly before cooking. Gently lower 5-6 mushrooms into the hot oil at a time. They should gently bubble and rise to the top. Once golden brown and crisp, remove with a slotted spoon and place on absorbent paper. Repeat this process to cook the remaining mushrooms, being careful not to overfill the saucepan.
Combine the salt and lime zest in a small bowl. In a separate bowl, combine the sour cream, jalapenos and 1 tablespoon of lime juice. Sprinkle the lime salt over the popcorn and serve with the jalapeno sour cream.