Grease a large microwave-safe mug with a light coating of coconut oil or avocado oil spray.
In a small bowl, whisk together the protein powder, oat flour, cacao powder, baking powder, and sea salt until no lumps remain.
Stir in the liquid egg whites, Greek yogurt, almond milk, and vanilla extract until the batter is smooth and thick.
Fold in half of the dark chocolate chips into the batter.
Pour the batter into the prepared mug, then drop the almond butter into the center, pressing it down slightly so it is covered by batter.
Sprinkle the remaining chocolate chips on top.
Microwave on high for 75 to 90 seconds, checking to ensure the edges are set while the center remains slightly soft.
Let the cake rest for 2 minutes before eating to allow the texture to firm up and the center to reach a molten consistency.