Preheat oven to 425F. Lightly grease a 12-cup muffin tin. Set aside.
In a medium bowl, combine flour, baking powder, and salt. Set aside.
In a separate large bowl, whisk sugar, melted coconut oil, eggs, yogurt, lemon juice, lemon zest, buttermilk, and vanilla until smooth. Gently fold flour mixture into liquid until just combined. Fill muffin tins to brim with batter and set aside for a moment to prepare the topping.
Make the topping: In a small bowl, toss all topping ingredients until crumbly and in pea-sized shapes. Sprinkle topping over muffin batter and gently press crumbs to adhere them to batter.
Bake muffins at 425F 5 minutes, then reduce heat to 375F and continue baking an additional 14-15 minutes until muffins test done with a toothpick. Cool muffins in pan 5 minutes, then transfer to a wire cooling rack. Enjoy muffins warm!