Combine first 6 ingredients in a small bowl; stir with a whisk until blended.
Heat vegetable oil in a large nonstick skillet over medium-high heat. Add green beans and onion; cook, stirring occasionally, 8 to 10 minutes or until beans are crisp-tender and lightly browned. Add snow peas and bell pepper strips; cook 3 minutes, stirring occasionally.
Stir soy sauce mixture with a whisk, and pour over vegetables; cook 1 minute, stirring constantly, until mixture thickens. Sprinkle with sesame seeds, and toss gently to coat. Serve immediately.