Melt butter in a medium saucepan over medium-low heat. Increase heat to medium, and stir in spaghetti, cooking until coated with the melted butter and lightly browned.
Stir onion and garlic into the saucepan, and cook about 2 minutes, until tender. Stir in jasmine rice, and cook about 5 minutes. Pour in vegetable broth. Season mixture with salt and pepper. Bring the mixture to a boil, cover, and cook 20 minutes, until rice is tender and liquid has been absorbed.
Place asparagus in a separate medium saucepan with enough water to cover. Bring to a boil, and cook until tender but firm.
Mix asparagus and cashew halves into the rice mixture, and serve warm.
