Peel yuca and cut into 1- to 1 1/2-inch pieces. Peel the calabaza and cut into 1- to 1-1/2-inch chunks. Peel the sweet potatoes and cut into 1- to 1 1/2-inch pieces.
In large Dutch oven, combine yuca and 1 cup water. Cover and simmer over medium-high heat for 5 minutes, turning the yuca pieces over once.
Add calabaza, sweet potatoes, green plantain, onion, garlic, bell pepper, cilantro, and salt. Toss all ingredients well and cover. Cook for 10 minutes. Cover and cook for 15 minutes, gently tossing the ingredients once. Add 3/4 cup of the coconut milk and toss the ingredients again. Cover and cook for another 2 to 3 minutes.
Stir in the remaining 1/4-cup coconut milk and carefully place the fish steaks over the vegetables. Pour several spoonfuls of the broth over the fish and top with some of the vegetables. Cover and cook until the fish is white and flaky, 10 to 12 minutes. Gently move the vegetables aside and remove the fish pieces, placing them on a large serving platter.
Spoon the vegetables and sauce alongside.