Preheat oven to 350°F (177ºC) and prepare parchment-lined loaf pan.
In a medium-sized mixing bowl, whisk together flour, baking powder, baking soda, cinnamon and salt and set aside.
In a large mixing bowl, cream together butter and sugar. Add eggs and vanilla and continue to mix until well combined. Fold in mashed banana.
Add half the flour mixture to the wet ingredients and stir just until the flour is mixed in. Fold in Greek yogurt, turning over 6-7 times.
Add 1 cup of the sliced strawberries (and the walnuts, if using) to remaining flour mixture and gently stir together just until the berries are covered with flour and evenly distributed.
Toss flour-covered berries into batter and stir it all together just until combined. The batter should still be lumpy with pieces of fruit and nuts scattered throughout, and you should still be able to see bits of flour. This will result in a lighter, fluffier texture.
Transfer batter to prepared loaf pan, smoothing it out with a rubber spatula if needed. Top with remaining ½ cup sliced strawberries.
Bake for 65-70 minutes until golden and a tester comes out clean. Let cool in loaf pan for 15 minutes, then lift from pan using parchment edges and transfer to a wire cooling rack. Let cool for another 45 minutes prior to serving.