Yes. Using an action granted by a spell is not the same as Casting a spell.
So on your first turn you could use your bonus action to cast Dragon's Breath and then use your action to use the granted breath attack. On your second turn you can again use your action to use the breath weapon again and then use Quicken Spell metamagic to cast Lightning Bolt as a bonus action.
if a sorcerer casts Dragon Breath to himself in "turn 1", he can exale the breath and cast Lightning Bolt quickened with metamagic in "turn 2"?
Thank you.
Yes. Using an action granted by a spell is not the same as Casting a spell.
So on your first turn you could use your bonus action to cast Dragon's Breath and then use your action to use the granted breath attack. On your second turn you can again use your action to use the breath weapon again and then use Quicken Spell metamagic to cast Lightning Bolt as a bonus action.
Yep. What Fangeye said.