In a bowl, stir together the butter, flour and sugar. Rub with your fingertips until the butter is incorporated, to have a crumbly texture. Mix in the oats and the seeds and then the water, oil and honey. stir everything together, resulting in awet, sandy texture. Set aside.
Preheat the oven to 170 °C.
Stir together the flour, baking powder, set aside. In a marge mixing bowl, lightly whisk together the eggs, sugar and melted butter (make sure it is not too hot . Whisk in the milk and orange zest.
Add the stifted dry ingredients and fold together very gently, add nuts and chocolate. Make sure you stir the mix just enough to combine; it should remain lumpy and rough.
Spoon the mixture into the muffin case to fill them up. Generously cover with the crumble topping. Bake for 30/35 minutes ou until a skewer inserted in the centre of a muffin comes out clean.