Slowly heat margarine, syrup, sugar, peanut butter and jam in a pot at low heat until the sugar is dissolved.
Finely chop the rice cakes. Chop mango and cranberries. Mix everything with oatmeal and amaranth in a bowl.
Pour the syrup-fat mixture into the bowl and stir well. Pour the muesli mixture into a springform pan (24 x 24 cm) lined with baking paper, press down firmly and allow to set in the fridge until the muesli bars have set.
Remove and cut into rectangles.