Cut the broccoli florets into 1-inch pieces and slice the stems crosswise into 1/2-inch-thick pieces. Put in a large bowl and toss with the oil and 1 tablespoon water. Spread on a baking sheet and roast, stirring once halfway through, until tender and lightly charred, 20 to 25 minutes. Transfer to a bowl and toss with the cashews, fish sauce, lime juice, cilantro and jalapeno. Serve with lime wedges.