Score the duck breast skin in a tight crosshatch pattern, ensuring you do not pierce the meat.
Season both sides of the duck generously with the sea salt and black pepper.
Place the duck breast skin-side down in a cold stainless steel or cast iron skillet.
Turn the heat to medium-low and cook for 10-12 minutes, allowing the fat to render slowly until the skin is deeply golden and crispy.
Flip the breast and cook for an additional 3-5 minutes until the internal temperature reaches 135 degrees F for medium-rare.
Transfer the duck to a cutting board and let it rest for at least 5 minutes before slicing.
Drain the excess duck fat from the pan, leaving about 1 tablespoon behind.
Add the minced shallot to the pan and sauté for 1 minute, then add the frozen cherries, balsamic vinegar, honey, and thyme.
Simmer the sauce over medium heat for 3-4 minutes, stirring frequently, until the cherries soften and the liquid reduces to a thick glaze.
In a separate skillet, quickly sauté the baby spinach with a splash of water until just wilted, then serve the sliced duck over the greens topped with the warm cherry glaze.