Stir together oats and 2 T warm water, let stand for 5 minutes. Meanwhile stir together 1/2 cup flour, sugar, baking powder, cinnamon and a Dash of salt. Stir egg yolk, oil and milk into oat mixture; add to dry ingredients, stirring just till moistened. Fold in 3 T of the walnuts and the raisins. Line four 6-ounce custard cups with paper baking cups. Fill 2/3rds full. Combine 2 t flour , brown sugar, butter, and remaining walnuts. Sprinkle atop muffins. Micro-cook, uncovered, on 100% power for 1 1/2 to 2 1/2 minutes or till done, rearranging twice. (When done, surface may still appear moist but a wooden pick inserted near the center should come out clean.) Remove from custard cups. Let stand on a wire rack for 5 minutes. Serve warm.