Yes, this works.

The only conditions for using Stunning Strike are:

• you hit
• with a melee weapon attack
• You spend 1 ki point

So when you make an opportunity attack, and hit with a melee weapon, you can spend 1 ki point to use stunning strike.

Yes, this works.

The only conditions for using Stunning Strike are:

• you hit
• with a melee weapon attack
• You spend 1 ki point

So when you make an opportunity attack, and hit with a melee weapon attack, you can spend 1 ki point to use stunning strike.

Yes, this works.

The only conditions for using Stunning Strike are:

• you hit
• with a melee weapon attack
• You spend 1 ki point

So when you make an opportunity attack, and hit with a melee weapon, you can spend 1 ki point to use stunning strike.

Notably, Stunning Strike requires a melee weapon attack, so unarmed strikes do not qualify.

Yes, this works.

The only conditions for using Stunning Strike are:

• you hit
• with a melee weapon attack
• You spend 1 ki point

So when you make an opportunity attack, and hit with a melee weapon, you can spend 1 ki point to use stunning strike.