Creating Streusel Stuffed Peach Muffins is simple if you follow these step-by-step instructions:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease it lightly.
2. Mix Dry Ingredients: In a large mixing bowl, whisk together 2 cups of flour, 1 cup of sugar, baking powder, baking soda, salt, and cinnamon until well combined.
3. Combine Wet Ingredients: In another bowl, combine the buttermilk, vegetable oil, and eggs. Mix until smooth.
4. Combine Mixtures: Gently fold the wet ingredients into the dry ingredients until just combined. Be careful not to overmix.
5. Add Peaches: Gently fold in the diced peaches until evenly distributed throughout the batter.
6. Prepare Streusel: In a separate bowl, combine ½ cup flour, rolled oats, brown sugar, and cinnamon for the streusel. Add the cold cubed butter and mix with your fingers or a pastry cutter until crumbly.
7. Fill Muffin Tin: Spoon the muffin batter into the prepared muffin tin, filling each cup about two-thirds full.
8. Add Streusel Topping: Generously sprinkle the streusel mixture on top of each muffin.
9. Bake: Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
10. Cool: Remove the muffins from the oven and let them cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

These straightforward steps will guide you to creating these delicious muffins effortlessly!