Preheat oven to 350℉. Spray a 9” springform pan with cooking spray and line the bottom with parchment.
In a medium bowl whisk together flour, baking soda, baking powder, and salt. In a second medium bowl mix together banana, yogurt, and vanilla.
In a large bowl or the bowl of a stand mixer fitted with the paddle attachment, beat butter, sugar, and Stevia In The Raw® together until fluffy, about 5 minutes. Beat in eggs 1 at a time until combined. Add flour mixture in 2 parts, alternating with banana mixture. Beat on low until just combined. Fold in toffee.
Scrape batter into pan, smooth top, and bake until a toothpick inserted in the center comes out clean, about 45 minutes. Cool 30 minutes, then run a thin knife around edge of pan and remove pan ring. Cool completely, then transfer cake to a serving platter or cake stand.
In a food processor combine cream cheese, butter, and vanilla. In a small bowl whisk together Stevia In The Raw® and cornstarch and add to processor. Pulse until very smooth. Frost top of cake, leaving sides bare.
In a medium nonstick skillet melt butter over medium. Add sliced banana and cook, flipping slices once, until browned and caramelized on both sides, about 2 minutes per side. Cool completely, then arrange on top of frosted cake.