Step 1

Pierce the squash several times with a fork or knife. Place the squash and water in a 6-quart slow cooker. Cover and cook on LOW until the squash is tender, 5 to 6 hours.

Step 2

Remove the squash, and let cool slightly. Cut the squash in half lengthwise. Scoop out and discard the seeds. Using a fork, scrape the insides of the squash shells to remove the spaghetti-like strands to yield 3 to 4 cups. Return the spaghetti squash shells to the slow cooker, cut-sides up. Set the squash strands aside.

Step 3

Heat the oil in a large skillet over medium-high. Add the garlic and tomatoes; cook, stirring often, until the tomatoes begin to soften, about 3 minutes. Remove from the heat. Add the squash strands, beans, basil, and salt to the tomato mixture, stirring to combine. Gently fold in the mozzarella.

Step 4

Spoon the squash mixture evenly into each squash half in the slow cooker. Cover and cook on LOW until the cheese is melted and the mixture is heated throughout, about 1 hour. Garnish with the basil leaves, if desired.