How to make a healthy cake with oats, pumpkin and nuts

Ingredients:

60g sweetener(stevia or your choice)¼ cup
70g melted and cooled butter(¼ cup)
200g pumpkin puree
90g rolled oats(1cup)
6g baking powder(½ tbsp)
1 teaspoon cinnamon
60g chopped walnuts(½ cup)
3 eggs(separate the yolks from the whites)
salt
40 minutes at 180°C/ 360°F