Preheat oven to 375°.
Weigh or lightly spoon 1 1/4 cups baking mix into dry measuring cups; level with a knife. Combine baking mix and brown sugar in a medium bowl; stir with a whisk. Make a well in center of mixture. Combine milk and next 3 ingredients in a bowl, stirring well with a whisk. Add to baking mix mixture; stir just until moist.
Place 12 muffin cup liners in muffin cups. Combine diced strawberries and 1 teaspoon baking mix; toss lightly. Spoon half of batter evenly into liners. Top each with 1 teaspoon diced strawberry mixture. Spoon remaining batter evenly over strawberries. Place 1 strawberry slice on top of each muffin.
Bake at 375° for 14 minutes or until muffins spring back when touched lightly in center. Cool in pans 5 minutes. Remove from pans; serve warm.
We tossed the strawberries with a teaspoon of gluten-free baking mix and added them between two layers of batter to keep them from sinking to the bottom as the muffins bake. The strawberry slices on top are a pretty way to finish them off.
Cooking Light Gluten-Free Cookbook