In a skillet on medium-low heat, toast all the spices, except the oregano, for about 5 minutes or until fragrant. Allow to slightly cool and transfer to a spice grinder or mortar and pestle. Grind into a powder.
In a blender, combine the citrus juices, garlic, oregano, ground spices, and salt.
Cover the ribs with the mixture, and let marinate for at least 1 hour or overnight.
Line a slow-cooker or roasting pan with banana leaves. Place the ribs and marinade inside, and cover with another banana leaf.
Cover and cook on low for 6 hours or high for 4 hours. If roasting in an the oven, cook at 325F for 4 hours.
6. Remove ribs from the slow cooker and transfer to a banana leaf-lined baking sheet. Broil for about 6-8 min, or until the surface is browned.