Bring a large pot of salted water to a boil. Wash and dry produce. Trim and thinly slice mushrooms (skip if your mushrooms are pre-sliced!). Halve, peel, and thinly slice shallot. Peel and mince or grate garlic. Finely chop sun-dried tomatoes. Finely chop parsley. Quarter lemon.
Once water is boiling, add rigatoni to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. Reserve ¾ cup pasta cooking water (1 cup for 4 servings), then drain.
While pasta cooks, heat a drizzle of oil in a large pan over medium-high heat. Add mushrooms and shallot; cook, stirring occasionally, until veggies are browned and slightly crispy, 6-8 minutes. Season with salt and pepper.
Add garlic, sun-dried tomatoes, tomato paste, and sugar to pan with veggies. Cook, stirring, until tomato paste is brick red and garlic is fragrant, 1-2 minutes. Stir stock concentrate and 1⁄3 cup reserved pasta cooking water (½ cup for 4) into pan. (TIP: Ladle directly from pasta pot if pasta isn’t finished cooking yet.) Bring to a simmer and cook until sauce has slightly reduced, 1-2 minutes. Reduce heat to low and stir in hummus and a large drizzle of olive oil until fully incorporated. (TIP: Add another splash of pasta cooking water if sauce seems dry.) Season with salt and pepper.
Add drained rigatoni and half the parsley to pan with sauce; stir until coated. TIP: If necessary, add another splash of reserved pasta cooking water and another drizzle of olive oil until everything is coated in a glossy sauce. Taste and season with salt and pepper if needed.
Divide pasta between bowls. Top with almonds, remaining parsley, and as many chili flakes as you like. Squeeze juice from one lemon wedge (two wedges for 4 servings) over top. Serve with remaining lemon wedges on the side.