In a medium bowl, whisk together all of the ingredients for the creamy mustard vinaigrette. Season to taste with salt and black pepper, cover and refrigerate until you are ready to use.
Add the cooked ditalini pasta to a large bowl. Set aside.
In a large nonstick skillet set over medium-high heat, add the sausage. Cook until brown and cooked through, about 10 minutes. Remove from heat and transfer to the bowl with the pasta.
Also to the bowl add the baby spinach, sweet peas, the creamy mustard vinaigrette and salt and black pepper to taste. Toss thoroughly to evenly distribute the ingredients. Transfer to a serving platter and garnish with sliced sugar snap peas and cotija cheese. May be served warm or cold.