Cook the pasta shells in salted water until al dente. Drain and while it begins to cool, make the dressing and prep additional ingredients.
In a blender, combine kefir, olive oil, garlic, salt, cayenne pepper and 1 cup of the peas. Blend until smooth and pale green.
Chop the green onions into thin slices. Stack the mint leaves and slice crosswise into thin ribbons. Dice the cheese into ¼ inch cubes or crumble if using feta.
In a large mixing bowl, combine pasta, dressing, green onions, mint, cheese and remaining peas and stir to combine. Refrigerate a few hours or overnight before serving. If the pasta absorbs the dressing, add more kefir before serving.