Whisk together eggs, oil, mashed bananas, and vanilla essence until well combined using an electric beater or whisk.

Sieve together whole wheat flour, baking powder, and baking soda.

Gradually fold the dry ingredients into the wet mixture, adding one spoon at a time.

Add oats and milk to the mixture while folding it in gently.

Mix until well combined, checking for a smooth, pourable consistency. Add more milk if needed to achieve the right consistency.

If desired, add honey to increase sweetness, especially if the bananas aren't very ripe.

Grease a microwave-safe bowl or cake tin with oil.

Pour half of the cake mixture into the prepared tin.

Sprinkle half of the chocolate chips over the mixture.

Pour the remaining cake mixture into the tin, covering the chocolate chips.

Garnish the top of the cake with oats, remaining chocolate chips, and chopped walnuts.

Microwave for 4-6 minutes. After 4 minutes, check for doneness by inserting a toothpick or knife into the center. If it comes out clean, the cake is done.

Alternatively, preheat an oven to 325°F (160°C) and bake for 30 minutes.

Let the cake cool down to room temperature before slicing and serving. It tastes best when served warm.