Preheat the oven to 375ºF and wipe a 9x9-inch pan with butter. Set aside.
If using frozen rhubarb, be sure to thaw it out. Then, add all of the ingredients for the filling to a large bowl and toss until the rhubarb is coated. Set aside.
Prepare the crisp topping by adding the oats, flour, sugar, salt, orange zest, almond extract, and almonds to a large bowl.
Add the butter and use a fork (or your hands) to cut it into the dry ingredients until a crumble forms. This will take 3-4 minutes.
Transfer the rhubarb to the pan and top with half of the oatmeal topping. Gently work half of the oatmeal, topping down into the rhubarb with a spatula. Add the remaining oatmeal topping and cover.
Bake for 30 minutes, uncover, and bake for an additional 20-30 minutes or until the top is golden brown and the edges begin to bubble.*
Remove from the oven and let it rest for 10 minutes before serving. Serve with a scoop of vanilla ice cream or whipped cream.