Peanut Butter Chocolate Chunk Banana Cake

creamy peanut butter

canola, vegetable, or melted coconut oil

large egg

to 6 ounces banana or vanilla Greek yogurt (plain Greek yogurt or sour cream may be substituted)

granulated sugar

vanilla extract

mashed banana (about 2 medium, ripe bananas)

+ 2 tablespoons all-purpose flour

baking powder

salt, optional and to taste

creamy peanut butter, for swirling on top

about 4 ounces dark chocolate, roughly chopped (semi-sweet chocolate chips may be substituted)