Bring a large pot of salted water to a boil and cook the whole grain linguine until al dente, usually about 8-10 minutes.
While the pasta is cooking, season the chicken breast evenly with sea salt and black pepper on both sides.
Heat the olive oil in a large skillet over medium-high heat and sear the chicken until golden brown and cooked through, approximately 6 minutes per side.
Transfer the chicken to a cutting board and allow it to rest for 5 minutes before slicing into thin, bite-sized strips.
In the same skillet used for the chicken, add the minced garlic and sun-dried tomatoes, sautéing for about 1 minute until the garlic is fragrant.
Reduce the heat to low and add the cooked linguine, sliced chicken, baby spinach, and basil pesto to the skillet.
Gently toss all ingredients together until the spinach is wilted and the pasta is thoroughly coated in pesto, adding a tablespoon of pasta water if needed for moisture.
Squeeze the fresh lemon juice over the pasta for a bright finish and serve immediately.