Cut the bread into 1-inch pieces; place in a large mixing bowl.
In a saucepan, bring the cashew milk to a simmer. Remove from heat and add the tea bags. Let the tea steep for 5 minutes, then discard the bags. Transfer the cashew milk to a blender. Add the banana, brown sugar, chia seeds, vanilla, and spiced; blend until smooth. Pour the liquid over the bread; turn to coat.
Transfer the bread and any extra liquid to a 9x13-inch casserole dish. Cover and refrigerate overnight.
The next morning, heat the oven to 350ºF.
In a small bowl, combine the butter, brown sugar, agave, and spices; mix with a form until the mixture is crumbly. Stir in the cashews. Spread the topping over the uncovered casserole.
Bake 30 minutes, or until puffed and golden brown.