Mix butter and brown sugar until thoroughly blended. Add eggs and vanilla, beat well. In another bowl, combine oats, flour, salt, and baking powder. Blend oat mixture with butter mixture. Stir in walnuts, coconut, and raisins.
Pack cookie dough into an ice cream scoop (4 oz size) or 1/2 cup measuring cup. Scrape dough level with rim and empty onto lightly oiled baking sheets, spacing dough about 3 inches apart. Back at 350 degrees until cookie edges are golden brown, about 20 minutes. If using one oven, switch pans halfway through baking. Cool cookies on rack, serve or store airtight up to two days.