Bring a medium pot of salted water to a boil over high heat. 

Wash and dry produce.

Trim and halve zucchini lengthwise; cut crosswise into ¼ -inch-thick half-moons. Quarter lemon. Finely chop chives. 

Once boiling, add pasta to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. Reserve 1 cup pasta cooking water (2 cup for 4), then drain.

While pasta cooks, open package of chicken and drain off any excess liquid. Heat a drizzle of oil in a large pan over medium-high heat. Add chicken in a single layer and season with salt and pepper. Cook until browned 3 minutes.

Add zucchini and continue to cook, stirring occasionally, until zucchini is lightly browned and chicken is cooked through, 2-3 minutes more.

In a small bowl, whisk together smokey mustard, vegetable stock concentrate, cream cheese, juice from 1 lemon wedge, and 1/4 cup pasta cooking liquid (juice from 2 lemon wedges and 1/2 cup pasta cooking liquid for 4) Ladle pasta cooking liquid directly from the pot if pasta is still cooking.

Lower heat to low and add mustard mixture. Simmer, stirring constantly until warmed through and thoroughly combined, 1-2 minutes. Add splashes of pasta cooking liquid as needed. 

Add cooked pasta. Toss to combine and taste and season with salt, pepper, and another squeeze of lemon if desired.

Divide pasta between shallow bowls and top with chives. Serve.