- Bring broth and water to simmer in saucepan over medium heat. Remove from heat, cover, and keep warm.
- Heat 2 teaspoons oil in medium saucepan over medium heat until shimmering. Add mushrooms and ¼ teaspoon salt and cook, covered, until just starting to brown, about 4 minutes. Transfer mushrooms to bowl and set aside. Return now-empty pot to medium heat, add remaining 2 teaspoons oil, and heat until shimmering. Add onion and ¼ teaspoon salt and cook until just beginning to soften, about 2 minutes. Add rice and cook, stirring constantly, until grains are translucent around edges, about 1 minute.
- Stir in 1½ cups broth, cover, reduce heat to medium-low, and simmer until almost all liquid is absorbed, about 12 minutes. Stir in asparagus, cover, and cook 2 minutes longer. Add ½ cup broth and cook, stirring constantly, until broth is absorbed, about 3 minutes. Add remaining ¼ cup broth and peas and cook, stirring constantly, until rice is creamy and al dente, 3 minutes longer.
- Off heat, stir in cooked mushrooms, cover, and let sit for 2 minutes. Stir in Parmesan, basil, butter, and lemon juice. Season with salt and pepper to taste. Serve, passing extra Parmesan.
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