Melt the margarine in a small pan over low heat. Add the serrano pepper and cashews and saute for 2 minutes. Add the peanut butter and stir until melted, then add the sugar. Stir well and remove from the heat.

A butternut squash has a cavity at the blossom end and a long solid section that extends to the stem. Using a paring knife, make several 1/4 inch / 7 mm cuts in the flesh extending from the cavity to the stem end. Place the squash halves in a baking dish and cover the cut surface with the nut mixture. Divide the remaining nut mixture between the two cavities.

Bake for 60 to 70 minutes, or until a fork can be easily inserted through the skin into the solid section of squash.