Make the pimento cheese spread. In a medium bowl, combine mayonnaise, Cheddar, pimento peppers and cream cheese. Stir until evenly combined. Season with salt and pepper to taste. In a 9x13-inch baking dish, lay down the bottom halves of the mini-rolls. Spread the pimento cheese spread on top of the bread and evenly lay ham slices on top of the pimento layer. Top with more pimento spread, then place the other halves of the rolls on top. Brush the bread with melted butter. Sprinkle with poppy seeds, garlic powder and salt. Cover with foil and bake for 10-15 minutes, until the cheese begins to melt and rolls are golden. For a more toasted bun, uncover the pan during the last few minutes of baking.