Such a cooktop can then be connected in two main ways:

• Single phase, both "L"s jumpered together and connected to the line wire, all of that on a single-phase circuit.
  The two halves of the cooktop are thus wired in parallel !!!
  Given that circuits are pretty much always limited!!!! to 16 Amper !!!!!
  This limits the total!!!! power available.
  
  Old-school traditional cooktops would trip the breaker when you turn all the zones on to max power,
  modern induction cooktops can typically!!! be programmed to limit!!!! the total power.
  
  
• Two phases, each connected to one "L" terminal and supplying one half of the cooktop.
  This gives you nearly 7.4 kW total, which is pretty much enough for everyone.

I've never seen a cooktop that would be really connected in a delta-like fashion, using the 400 V phase to phase voltage.
"400 V" is just a supposedly customer-friendly shorthand for "three-phase service".