Bring a large pot of salted water to a boil. Add pasta and cook, stirring occasionally, until pasta is al dente, 9-11 minutes. Reserve ½ cup pasta cooking water (per 2 servings). 1 cup if scaling up to 4 servings), then drain.
While pasta cooks, prepare the other ingredients. Trim and discard woody ends from asparagus. Cut the stalks crosswise into 1-inch pieces. Dice tomato. slice the scallions, separating green from white. Zest the lemon and then cut the lemon into quarters.
Melt 1 tablespoon of butter (2 TBSP for 4 servings) in a large pan over medium-high heat. Add panko and almonds; season with salt and pepper. Cook, stirring, until golden brown, 3-4 minutes. Turn off heat and stir in a pinch of lemon zest and a pinch of chili flakes. Transfer to a small bowl.
Heat 3 of olive oil in same pan over medium-high heat. Add asparagus and the scallion whites and cook, stirring, until bright green and tender, 2-4 minutes.
Add tomato and cook, stirring, until slightly softened, 1-2 minutes. Season with salt and pepper.
Turn the heat down to low. Add 2 tablespoons butter (4 TBSP for 4 servings), Parmesan cheese, reserved pasta water, half the green scallion, remaining lemon zest, and as much chili flakes as you like to pan. Cook, stirring, until pasta is coated in sauce, 1-2 minutes.
Stir in a squeeze of lemon juice to taste. Season with salt and pepper to taste.
Divide pasta between bowls. Sprinkle with panko mixture and remaining Parmesan. Garnish with scallion greens. Serve with remaining lemon wedges on the side.