Preheat the oven to 425°F and line a 12-count muffin tin with paper liners, or spray them with baking spray before setting the tin aside.
Stir together the flour, baking powder, salt, and cinnamon in a medium mixing bowl, set aside.
Whisk together the oil and sugar until combined, in a large mixing bowl.
Add the eggs into the wet ingredients and whisk until smooth.
Then, add the sour cream and vanilla, and whisk until smooth.
Next, add the dry ingredient mixture to the wet ingredients and stir them together until they're just combined, with no dry patches.
Then, add in the milk to the batter and stir until well incorporated.
Add the chopped peaches to the batter and fold them in.
Divide and pour the batter among the 12 muffin sections, set aside.
In a medium-sized bowl stir together the sugar and butter until combined. Add the flour and salt, and mix until combined and crumbly to make the streusel.
Evenly add the streusel over each of the muffins, it looks like too much but it’s not, use it all.
Bake muffins at 425°F for 5 minutes. Then, reduce the heat to 350°F and bake for an additional 16-18 minutes or until a toothpick can be inserted into the center of a muffin and it comes out mostly clean.
Let the muffins cool in the tin for 5 minutes then carefully take them out and let them cool completely on a wire rack. Serve warm or at room temperature.