To seed a cucumber, cut it in half lengthwise and scoop out the seeds with a teaspoon, a melon baller or simply the back of your peeler.
For a bell pepper, which has four walls like a box, use a chef's knife to trim off the sides. What remains is the seeds attached to the stem.
To seed a tomato, cut it in half through its equator. Then, over a bowl, use your fingers to pop out the seeds. If you do this technique over a strainer, you will strain out the seeds to collect the tomato juice.