Whisk together the soy sauce, water, maple syrup (or honey/brown sugar), cornstarch, sesame oil, and minced garlic in a liquid measuring cup or small bowl until smooth; set the sauce aside.
Heat a large nonstick skillet or wok over medium-high heat and add 1 tablespoon of canola oil.
Add the ground beef, sprinkle with the kosher salt and black pepper, and break it up with a wooden spoon; cook until browned and fully cooked, about 5 to 7 minutes.
Use a slotted spoon to transfer the cooked beef to a plate, leaving any excess fat in the pan; wipe the skillet clean with a paper towel.
Add the remaining 1 tablespoon canola oil to the skillet, then add the sliced bell pepper, prepared carrot, and trimmed green beans; cook, stirring often, until the vegetables are crisp-tender, about 4 minutes.
Add the minced ginger and red pepper flakes and cook until fragrant, about 30 seconds, then stir in the white and light-green parts of the sliced green onions.
Return the cooked beef to the skillet, pour the reserved sauce over everything, and stir constantly until the sauce thickens and coats the beef and vegetables, about 1 to 2 minutes.
Stir in the dark green tops of the green onions, sprinkle with sesame seeds if using, taste and adjust seasoning, and serve hot with cooked rice.
