For the black bean salsa: Toss together the black beans, pimentos, lime zest and juice, onion, cilantro and salt to taste in a bowl. Set aside.
For the tostadas: Preheat a waffle iron.
Mix the hash browns with the pepper jack, butter and salt and pepper to taste in a large bowl. Spray the waffle iron with cooking spray. Scoop a generous cup of the hash brown mix into each well of the waffle iron and cook until well browned and crispy, about 5 minutes. Set aside, keeping covered with a towel to keep warm.
For the toppings: Place a nonstick skillet over medium heat and add some butter. When melted, fry the eggs sunny-side up until the whites are set, about 3 minutes.
Place a hash brown tostada onto a plate and top with a fried egg. Spoon over some black bean salsa along with some guacamole, salsa, sour cream and a drizzle of hot sauce, then dive in.