Place ½ cup basil, olive oil, walnuts, salt, lemon juice, and garlic in a food processor or blender. Cover and process or blend until smooth. Reserve 2 tablespoon pesto for serving; set pesto aside.

Heat vegan butter and chili oil in a large nonstick skillet over medium heat. Add baby bella and shiitake mushrooms; cook 8 minutes, stirring occasionally. Add tomatoes; cook 5 to 7 minutes or until mushrooms are golden and cherry tomatoes begin to blister. Add remaining pesto to mushroom mixture and toss to coat. Remove from heat.

Cook pasta in a large saucepan in boiling salted water according to package directions. Drain pasta, reserving ½ cup pasta water.

Return pasta to saucepan. Add reserved pasta water and vegan sour cream; stir until combined. Gently stir in spinach and mushroom mixture. Transfer to 6 serving plates. Garnish with crushed red pepper, lemon zest, sliced basil, and reserved 2 tablespoon pesto, if desired.