Preheat the oven to 350 degrees F (175 degrees C). Grease a 12 cup muffin tin, or line with paper liners.
In a medium bowl, stir together the yogurt, 2 tablespoons of melted butter, oil and egg. In a large bowl, stir together the flour, 3/4 cup of brown sugar, baking soda and salt. Pour the wet ingredients into the dry, and mix until just blended. Fold in rhubarb. Spoon into the prepared muffin tin, filling cups at least 2/3 full.
In a small bowl, stir together 1/4 cup of brown sugar, cinnamon, nutmeg, almonds, and 2 teaspoons of melted butter. Spoon over the tops of the muffins, and press down lightly.
Bake for 25 minutes in the preheated oven, or until the tops spring back when lightly pressed. Cool in the pan for about 15 minutes before removing.