Cut the cucumber into thirds and then cut each piece in half lengthwise and remove the seeds using a spoon. Thinly slice the cucumber halves, place them in a large bowl, and set aside.

Next, peel and thinly slice the onion, lengthwise and add it to the bowl with the cucumber.

Cut the red bell pepper from around the seeds and membrane then thinly slice the pieces into long thin strips and add them to the bowl as well.

Peel the mangos then cut the fruit off the seeds. Discard the seeds and thinly slice the mango pieces into long, thin strips then add them to the bowl.

Add the basil to the bowl and toss everything to combine.

In a small bowl or jar, whisk to combine the vinegar, olive oil, chili flakes and salt together and then pour it over the salad and toss to combine.

Serve immediately with fresh basil leaves, for garnish, if desired.