Add the cilantro, parsley, salt, red pepper, vinegar, and beer to a food processor, process until well combined. While the food processer is running, slowly add the olive oil.
Add the diced avocado to a bowl, pour the chimichurri mixture over the avocado, and gently stir to combine.
Heat the grill to medium-high.
Drizzle the halloumi and red pepper with olive oil. Add the halloumi and red pepper to the grill. Cook the halloumi on both sides until grill marks appear, about 3 minutes per side.
Cook the red pepper until the skin has blackened.
Scrape the skin off the red pepper, remove the stem and seeds, and slice.
Fill the slider buns with cheese, top with sliced red peppers, and avocado chimichurri.